Varistor components are electrical components having an electrical resistance that depends on the voltage applied to the component. It is possible that the resistance decreases with increasing applied voltage. A varistor component can have a resistance in the kΩ, MΩ or GΩ range when a voltage of a normal operation condition is applied to the component. If the applied voltage exceeds a critical voltage, then the component's resistance may be reduced to the range of a few ohm.
Such varistor components can be utilized as compensation elements in circuits or to protect sensitive circuits against excessive voltages. When used as a protection device, the varistor component can be electrically connected between a circuit and a ground potential and shunt potentially damaging electric power.
As a result, the electric power dissipating in varistor components may exceed critical values when the varistor component becomes low ohmic at high voltages and the dissipated power can destroy the varistor component or even destroy the whole electrical circuit, including the whole electrical device having the varistor component. When critical voltage conditions are exceeded, a varistor component may even catch fire.
From U.S. Patent Application Publication No. 2001/0055187 A1, severally protected metal oxide varistor components are known. A varistor component comprises a fuse and an insulating gap can be created when normal operation conditions are left.
From U.S. Patent Application Publication No. 2009/0027153 A1, further metal oxide varistor components are known. Again, a fuse is utilized to open the circuit to prevent further damage when normal operation conditions are left.
However, known varistor components with a meltable material establishing a fuse cannot guarantee that the fuse's material maintains an electrical connection after melting. Especially in environmental conditions where the orientation of varistor components or where the components are subject to accelerations, the place where the material of the fuse will flow to is unknown and the risk of maintaining an electrical connection exists.